1. Field of the Invention
The present invention relates to a pattern inspection apparatus and a pattern inspection method. For example, it relates to an inspection apparatus and a method thereof which inspect a pattern by using a line sensor.
2. Description of Related Art
In recent years, with an increase in high integration and large capacity of a large-scale integrated circuit (LSI), a circuit line width required for semiconductor elements is becoming narrower and narrower. These semiconductor elements are manufactured by exposing and transferring a pattern onto a wafer to form a circuit by means of a reduced projection exposure apparatus (a so-called stepper or scanner) while using a master or “original” pattern (also called a mask or a reticle, and hereinafter generically called a mask) on which a circuit pattern is written, “drawn” or “formed”. Therefore, in order to manufacture a mask for transfer printing a fine circuit pattern onto a wafer, an electron beam pattern writing apparatus capable of writing a fine circuit pattern needs to be employed. The pattern circuit may be directly written onto a wafer by the pattern writing apparatus. In addition to the writing apparatus using electron beams, a laser beam writing apparatus which uses laser beams to write a pattern is also under development.
Since a lot of manufacturing cost is needed for the production of LSI, an improvement in yield is a crucial issue. However, as typified by a DRAM (Dynamic Random Access Memory) of 1 giga-bit class, the order of a pattern constituting the LSI has been changing from submicron to nano-meter. Then, one of major factors that decrease the yield is a pattern defect of a mask used in exposing and transferring an ultrafine pattern onto a semiconductor wafer by a photolithography technique. In recent years, with miniaturization of an LSI pattern formed on a semiconductor wafer, dimensions to be detected as a pattern defect have become extremely small. Therefore, a pattern inspection apparatus for inspecting defects of a transfer mask used in manufacturing the LSI needs to be highly accurate.
In the meanwhile, with development of multimedia technologies, the size of a liquid crystal substrate of an LCD (Liquid Crystal Display) is becoming large, e.g., 500 mm×600 mm or more, and a pattern of a TFT (Thin Film Transistor) or the like formed on the liquid crystal substrate is becoming minute. Therefore, it is increasingly required to inspect an ultra-fine pattern defect in a large area. For this reason, development of a pattern inspection apparatus which efficiently, in a short time, inspects defects of a pattern of a large-area LCD and a photomask used in manufacturing the large-area LCD is urgently required.
As an inspection method, there is known the method of comparing an optical image captured by photographing a pattern formed on a target workpiece or “sample”, such as a lithography mask, at a predetermined magnification by use of a magnification optical system with design data or an optical image captured by photographing the same pattern on the target workpiece. For example, the following is known as pattern inspection methods: “die to die inspection” that compares optical image data obtained by capturing images of the same patterns at different positions on the same mask, and “die to database inspection” that inputs writing data (design pattern data), which is generated by converting pattern CAD data into an appropriate format to be input by a writing apparatus when writing a pattern on a mask, into an inspection apparatus, generates design image data (reference image) based on the input writing data, and compares the design image data with an optical image serving as measurement data obtained by capturing the image of the pattern. In the inspecting methods of the inspection apparatus, the target workpiece is placed on a stage to be scanned by a flux of light while the stage is moving to perform inspection. The target workpiece is irradiated with a flux of light from a light source and an irradiation optical system. Light transmitted through the target workpiece or reflected by the target workpiece is focused on a sensor through the optical system. The image captured by the sensor is transferred to a comparison circuit as measurement data. In the comparison circuit, after position alignment of the images, the measurement data and the reference data are compared based on an appropriate algorithm. When the measurement data is different from the reference data, it is judged that there is a pattern defect (refer to, e.g., Japanese Unexamined Patent Publication (JP-A) No. 2007-102153).
In the conventional pattern inspection apparatus, a line sensor in which a plurality of light receiving elements, for example, for 512 pixels are arrayed perpendicularly to the direction of inspection is used for capturing an optical image of an inspection target workpiece. However, as for each element arranged in the line sensor, there is variation of optical properties among the elements. In particular, elements at the sensor end have large variation of the properties compared with elements at the inner side. Therefore, if the inspection is performed accepting a light quantity received by each element without question, there is a possibility of inducing a pseudo defect.
As mentioned above, in the sensors, such as a line sensor, in which a plurality of light receiving elements are arranged, there is optical properties variation among the elements. Specially, elements at the sensor end have large variation of optical properties compared with elements at the inner side. Therefore, if a light quantity received by each element is used as it is as measurement data, there is a problem that errors of measurement data will become large. Consequently, there occurs a problem of inducing a pseudo defect when such measurement data is used for inspection.